Multiple wave generators for harmonic drive



May 15, 1962 c w. MUSSER 3,

MULTIPLE WAVE GENERATORS FOR HARMONIC DRIVE 2 Sheets-Sheet 1 Filed June 6, 1961 Inventor C Wzlton Musser' By his Attorney May 15, 1962 c w. MUSSER MULTIPLE WAVE GENERATORS FOR HARMONIC DRIVE Filed June 6, 1961 2 Sheets-Sheet 2 Inner Hex-spine Ratios for/rranyement of 5' 1 Raf tax 4H2: zqelmnf offi'g. 5

The present invention relates to harmonic drives and particularly to such harmonic drives having multiple wave generators.

A purpose of the invention is to provide a harmonic drive which has a low ratio.

A further purpose is to reduce the amount of deflection in a harmonic drive for a given ratio.

A further purpose is to produce a harmonic drive (that is, gearing deflected according to a wave form as later explained) which is particularly well suited for use with flexsplines of large diameters.

A further purpose is to employ dual fiexsplines and a wave generator which by its motion acts on both flexsplines.

A further purpose is to develop two cooperating flexsplines by wave generators of elliptoidal shape in which the elliptoids are 90 out of phase.

A further purpose is to employ two wave generators each of which is of elongated contour and at one end is of circular shape and adapted to connect with cooperating members.

A further purpose is to employ two fiexsplines which have teeth which cooperate with one another and which also have teeth which cooperate with teeth on circular anchors, and to deflect both flexsplines by a duplex wave generator.

Further purposes appear in the specification and in the claims.

in the drawings I have chosen to illustrate a few only of the numerous embodiments in which the invention may appear, selecting the forms shown from the standpoints or" convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

FIGURE 1 is a diagrammatic fragmentary axial section of a harmonic drive according to the present invention.

FIGURE 2 is a plan diagram illustrating the action of an elementary elliptoidal shape which is being rotated.

FIGURE 3 is a plan diagram illustrating the action of the two fiexsplines and the duplex wave generator which is being rotated.

FEGURE 4 is a set of curves which explains the operation of the device of FIGURES l to 3 and also explains the device of FIGURES 5 and 6.

FIGURE 5 is a diagrammatic fragmentary axial section showing a modified harmonic drive according to the invention.

FIGURE 6 is a plan diagram useful in explaining the harmonic drive of FIGURE 5.

Describing in illustration but not in limitation and referring to the drawings:

The broad principles of strain wave gearing or harmonic drive are set forth in my US. Patent No. 2,959,065, granted November 8, 1960, for Spline and Rotary Table, and in my U.S. Patent No. 2,906,143, granted September 29, 1959, for Strain Wave Gearing.

In some cases it is desired to have a lower ratio, and under such conditions particularly when manufacturing the device from steel, two flexsplines are very desirably employed.

The flexsplines can be used in such a manner that the action is additive, as will be explained in connection with FIGURE 1, and therefore the ratio can be made considerably smaller than for a single flexspline.

3,h34,375 Patented May 15, 1%62 Tie Approachingthe matter in a different way, two flexsplines can be used for reducing the amount of deflection of the fiexsplines for a given ratio. Thus for a given ratio the two flexsplines essentially halve the deflection, or for a given amount of deflection the two flexsplines halve the ratio.

The invention lends itself particularly for application to structures which have large diameters, of which tank turrets constitute a good example.

Referring to FIGURE 1, a tank. structure is there illustrated, consisting of a tank hull 20, which has turning within it a turret 21 interconnected by a turret ring bearing 22, having an outer race 23, an inner race 24, and antifriction bearing round elements (shown as balls) 25. The device of the invention permits 369 rotation of the tank turret.

The harmonic drive includes an outer flexspline 26 having generally radially directed interior teeth 27 around the circumference and a telescoping inner flexspline 28 having generally radially directed exterior teeth 30 around the circumference.

The fiexsplines 26 and 23 are elongated axially and have respectively circular support portions 31 and 32 which are flanged at 33 and 34 and anchored respectively to the hull and to the turret by bolts 35 and 36. The fianged ortions 33 and 34 serve to lock the bearing races 23 and 24in place.

The'portions of the flexsplines carrying the teeth 27 and 3d are deflected so as to be in contact at a plurality of circumferentially spaced points with intermediatepoints at which the teeth are out of contact and out of mesh. The teeth 27 and 3d are therefore conjugate in form so that intermesh of the teeth can take place at the points of contact. 27 is larger in number than the outwardly directed set of teeth 3d and the difference in the number of teeth is equal to (or; a multiple of) the number of points around the circumference at which the teeth are in contact, which is the same as the number of lobes on the wave generatoras later explained.

While it is possible to use three or more points of contact between the teeth, it is usually preferable to have the teeth in contact at two diametrally spaced points, and this can be accomplished by shaping the sets of teeth 27 and 3t} into elliptoids when viewed in plan. In this instance, therefore, the difference in number of teeth of the outer and inner set will equal two or a multiple thereof, and in any instance it will equal the number of contact areas or a multiple thereof.

It will be evident that the fiexspline 26, being fastened to the hull, will be essentially fixed rotationally, while the flexspline 28 which is connected with the turret will be essentially considered the driven'element.

At the end of the flexsplines where the teeth 27 and 30 are provided, a multiple or duplex wave generator '37 is provided. The wave generator in cross section is of chanthat at which the teeth 27 are located. The inside elliptoidal bearing race 40 cooperates with uniform antifriction bearing barrel-shaped elements 43 (suitably rollers) which engage an inner elliptoidal race 44 on the end of the flexspline 28 opposite to the teeth 30.

It will be evident that the ellipt'oidal shapes of the races 33 and 40 acting through the antifriction bearing barrel- The inwardly directed set of teeth shaped elements 41 and 43 are responsible for deflecting V .with pinion 46 on a combination motor and speed reducer 47.

By providing the two elliptoids of the races 33 and 44) so that the major axis of one in plan is atright angles to the major axis of the other in plan, the two Waves are 180 out of phase although the axes are 90 out of phase. In this arrangement the major axis of the inner fiexspline 28 or of its inner wave generator is coincident with the minor axis of the outer flexspline 26 or of its wave gen erator. Accordingly, to cause the teeth of the two flexsplines to be in intimate engagement; it isonly necessary for the two wave generatorsto pinch the two fiexsplines together at two diametrically opposite points.

The channel'construction of the wave generator hearing carrier is therefore very effective to maintain intimate tooth contact. No outside structure is required to lend rigidity to the Wave generator. The forces directed inwardly and outwardly are essentially balanced in the wave generator itself, the forces tending to separate the teeth being the same on one flexspline as on the other, so that the channel construction can easily hold the teeth of the flexsplines into contact at the points of contact.

Furthermore, since the maximum forces are only present where theteeth are in contact, the actual weight of the structure can be considerably lessened by reducing the wall thickness as required at other points. When advantage of this feature is taken, the actual weight of the multiple or duplex wavegenerator can be reduced con 7 siderably and the reflected inertia to the motor is conthat are produced when a shape is rotated within a tube;

and this will be evident particularly frommy Patent No.

r 2,959,065 above referred to. The long arrow 48 illustrates the rotation of the elliptoidal shape. This is the rotation of the major and minor axis of the shape and not the rotation of the periphery of the shape. When this motion occurs, instantaneous velocities occur all around the periphery. Some of these are velocities in one direction while others are velocities in the other direction. With the major axis at 59 and the minor axis at 51, various arrows have been placed around the outside of the elliptoidal shape 52 to indicate the nature of these velocities in relation to velocity 48. The lengths of these smaller arrows are intended to suggest the relative angular motion at these various points compared to the relative angular motion of the elliptoid itself. The maximum angular motion takes place at the major and minor axes as shown by arrows 53. As one examines other points, proceeding from the major and minor axis towards a point intermediate thereto, the motion diminishes as indicated by arrows 54 until at the 45 ,degree point there is' no angular motion whatsoever. It will also benoted that at the major axis the arrows 53 are in the direction of the motion of the elliptoid shape, and at the minor axis the arrows 53 indicate motion in direction opposite to the direction of the motion of the elliptoid shape.

, .a point on the flexspline periphery measured from the' 'Now let us consider that another Wave generator is 1 applied along with its fiexspline as'in FIGURE 1 so that arrow 48 still depictsthe rotation of the elliptoid shapes, and we need have only one arrow since both shapes turn together though they are out of phase. Let us assume that the outer flexspline is rotationally stationary and fixed at one end as in FIGURE 1. Hence, as the elliptoidal shape of the wave generator is rotated, the minor axis of the outer flexspline 26 will be moving in the opposite direction to the rotation of the wave generator as shown by arrows 53.

Now if the inner fiexspline 28 is deflected by its wave generator so that its major axis is coincident with the minor axis of the outerelliptoid as in FIGURE 1, and if the inner elliptoid is of such a size that its teeth are in intimate mesh and contact with the teeth of the outer flexspline, at the minor axis of the outer elliptoid and the major axis of the inner eiliptoid, although out of mesh and out of contact at intermediate points, as shown in FIGURE 3, it will be evident that the teeth at these contact points are splined together. If the outside flexspline is angularly moving, then the inner fiexspline at this same location must also be angularly moving the same amount or velocity. Hence, at the major axis of the inner elliptoid there .is an angnllar motion as indicated by the arrow 53' which is equal to the motion of the arrow 53 when the wave generator is rotated. However, in FIGURE 3 this arrow 53' and the arrow 53 are a combination of the major and minor axis arrows$3 of FIGURE 2, be

cause the inner flexspline at its major axis is connected to the outer flexspline at its minor axis.

The motion between two points on the periphery can be considered as relative. The motions indicated in FIG- URE 2 assume that the elliptoid shape 52 has a net angular velocity of zero-and that this condition is satisfied when the 45 pointshave a zero angular velocity. However, if the points of the periphery lying on the major axis were assumed to be angularly stationary, then the'45 points and the net peripheralvelocity would be equal to the velocity depicted by arrow 53 of FIGURE 2, but since it is relative motion it would be of opposite sign or direction to that at the major axis of FIGURE 2.

Since there is a relative motion in the opposite direction at the 45 degree point of the inner flexspline 28 of an amount equivalent to that which is now occurring at the minor axis, of the outer fiexspline 26, these two motions must be added together, and the amount of the motion or the velocity, whichever is being considered at the moment, will be greater at the 45 degree point than it would be if only one flexspline were being used and the major axis were held stationary. V In actual fact, since the two fiexsplines are splined to.- gether, the two motions or velocities are directly additive, and as a result, the ratio is half what it would be for one of these flexsplines with the same amount of deflection. This is indicated by arrows 55 in FIGURE 3 at the 45 degree points. a a

These relationships can be better understood by referring to FIGURE 4. The ordinate in each case is the ratio in other portions of this specification. It is plotted in this manner since the movement of the point on the flexspline is the variable under observation and the wave generator rotation is the contant. The uppermost graph illustrates th action of the outer or fixed flexspline as the wave generator is rotated. The abscissa represents the angle to vertical axis of FIGURE 3.

The major axis of the inner wave generator is at the minor axis of the outer wave generator. At this point on the minor axis of the outer flexspline the periphery is moving in the direction opposite to the direction of rotation of the wave generator, hence the initial point on the curve is negative. Ninety degrees from this the motion is positive because this corresponds to the major axis of the outer wave generator. This repeats through the rest of the circumference.

Considering now the second graph from the top, the inner flexspline is assumed to be fastened at the other end and for the purposes of this second curve it is assumed that the outer flexspline is not there. In this case the angular motion of peripheral points on the inner flexspline would be directly out of phase with the motion on the outer flexspline.

In actual fact, however, the inner and outer flexsplines are splined together at the place where the major axis of the inner flexspline and the minor axis of the outer flexspline are located. Hence, counterclockwise motion 53 in FIGURE 3 will produce counterclockwise motion 53' of the peripheral points on the major axis of the inner flexspline. This, then, is the motion of the major axis of the inner flexspline which will be superimposed on any motion produced by the periphery of the inner flexspline upon rotation of the shape. The motion of the two then becomes additive and the third graph is produced by adding the second graph to the minor axis velocity of the first graph. The net angular velocity of the inner flexspline will be the same as the velocity at the 45 cations. This shows the actual motion of the inner flexspline when the major axis is splined to the minor axis of the outer flexspline. With this series of instantaneous velocities, the ratio when the arrangement of FIGURE 1 is used is illustrated in this third graph.

In FIGURE 5 the outside hull of the tank is indicated with bearing 22 mounting turret 21. In this case the outer race 23 of the hearing has a set of interior anchor teeth 56, circular in plan, and the inner race 24 of the hearing has a set of exterior anchor teeth 57, circular in plan, and radially spaced from the teeth 56. The races are force fitted, one into the hull and the other into the turret, so that relative motion can be imparted by these anchor teeth. The outer flexspline 26 at a position cooperating with the anchor teeth 56 has external spline teeth 58 and the inner flexspline 28 at a position corresponding to the anchor teeth 57 has a second set of spline internal teeth 60. Both of the fiexsplines are deflected into elliptoids in plan, the major axis of the inner elliptoid corresponding to the minor axis of the outer elliptoid. The flexspline teeth 58 are in contact with the anchor teeth 56 at two diametrically spaced points and at intermediate points the flexspline teeth are out of contact and out of mesh. Likewise the flexspline teeth 60 are in contact with the anchor teeth 57 at two diametrically spaced points and at intermediate points are out of contact and out of mesh; The differencein the number of teeth between the anchor teeth and the cooperating flexspline teeth in each case is equal to or a multiple of the number of lobes in the wave generator or the number of points of contact. Here the dual wave generators are mounted on a separate antifriction bearing 61 fixed on the hull 20 for maintaining the proper relation with the teeth on the hearing races.

By examining the plan diagram in FIGURE 6, it can be seen that the outside circle represents the fixed anchor teeth 56 on hearing race 23 and the interior circle represents the driven anchor teeth 57 on the opposite bearing race 24. The two fiexsplines 26 and 28 interengage with one another in the manner previously described in FIG- URE 1 and also interengage respectively with the anchor teeth. The flexsplines, however, are not fastened to anything so that the teeth 58 on the outer fiexspline 26 will engage the outer anchor teeth 56 at the major axis and the teeth 60 of the inner flexspline 28 will engage the anchor teeth 57 in the other bearing race 24 at the minor axis. With this arrangement the ratio is considerably lower since the full efiect of the flexspline deflection is being used. For example, for a flexural stress level in a 6 FIGURE 1 were used there would be a 30 to 1 ratio with the same stress level, and with the system of FIG- URE 6 there would be a 15 to 1 ratio with the same stress level.

Thus it can be seen that the multiple wave generators working on a multiplicity of flexsplines can be made to markedly reduce the ratios without complication in the structure.

In operation it will be evident that in either of the forms of FIGURE 1 or FIGURE 5 as the dual wave generators rotate, they in effect rotate the elliptoidal wave shapes, in which the minor axis of one corresponds to the major axis of the other, and this causes the points of contact to advance rotationally one of the flexsplines. In. the form of FIGURE 5 the anchorage relationship is obtained by contact at moving contact points with the respective anchor teeth, whereas in the form of FIGURE 1 the fiexsplines are physically connected directly to the hull and the turret. The lower series of graphs in FIG- URE 4 show the instantaneous velocities around the periphery of the two fiexsplines. From this it can be seen that the output 57 has the highest angular velocity within the system.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a harmonic drive, a first fiexspline having radially directed teeth thereon, a second flexspline telescoping with respect to the first and having teeth thereon adapted to cooperate with the teeth on the first flexspline at a plurality of spaced points with intermediate points in which teeth of the first and second fiexsplines are out of contact and out of mesh, a first wave generator adapted to deflect said first fiexspline into contact with said second flexspline at said spaced points of contact and a second wave generator adapted to deflect said second fiexspline into contact with said first flexspline at said points of contact, the difference in the'number of teeth between the first fiexspline and the second flexspline being equal to or a multiple of said number of points of contact between the first and second flexsplines.

2. A harmonic drive of claim 1,. in which there are two points of contact between the teeth on the first and second fiexsplines. p

3. A wave generator of claim 2, in which the first wave generator conforms to an elliptoid and the second wave generator conforms to an elliptoid.

4. A harmonic drive of claim 3, in which the elliptoids of the first and second wave generators are out of of phase.

5. A harmonic drive of claim 4, in which the first and second wave generators are rigidly interconnected.

6. A harmonic drive of claim 4, in which the first and second wave generators comprise a ringof channel cross section havin a race of one wave generator at one side of the channel and a race of the other wave generator at the other side of the channel and antifriction bearing elements between each said race and one of the flexsplines.

7. A harmonic drive of claim 6 in which each of the fiexsplines is of circular cross section at a point axially remote from the wave generator.

8. A harmonic drive of claim 6, in combination with a second set of teeth on the first fiexspline, an anchor telescoping with respect to the first flexspline, of circular contour and having a plurality of teeth which contact the teeth of the first fiexspline at a plurality of spaced points with intermediate points at which the second set of teeth and the anchor teeth are'out of contact and out of mesh, a second'set of teeth on the second flexspline, a second anchor telescoping with'respect to the second fiexspline, of circular contour and having teeth which contact the second set of teeth on the second flexspline at a plurality of circumferentially'spaced points with intermediate points at which the second set of teeth on the second fiexspline and the second anchor teeth are out of \contact and out of mesh, the difierence between the number of teeth in the second set on each fiexspline and the corresponding number of teeth on the anchor being equal to or multipleof the number of spaced points at "which vthe second set of teeth and the corresponding anchor are in contact;

9 In a harmonic drive, a first fiexspline of elongated character which is circular at one end and elliptoidal at the opposite end, a first cooperating member adjoining the point at which the first fiexspline is circular, means for anchoring the circular part of the first flexspline to the first cooperating member, a set of teeth directed in- .wardlyon the elliptoidal end of the first fiexspline, a second flexspline disposed within the first flexspline, the second fiexspline being circular at one end and elliptoidal at the opposite end, a second cooperating member secured to the second fiexspline at the end at which it is circular, a set of teeth on the outside of the second flexspline at the end at which it is eliiptoidal which are in contact with the teeth'on the inside of the first flexspline at two spaced points with intermediate points at which the teeth are out of contact and out of mesh, a duplex wave generator having an elliptoidal race outside the elliptoidal end of the first fiexspline and having an elliptoidal race inside the elliptoidal end of the second fiexspline, having antifriction bearing elements interposed between the outside elliptoidal race and the elliptoidal end of. the first fleXspline and having antifriction bearing elements interposed between the elliptoidal race inside the 'elliptoidal end of the second'flexspline and the elliptoidal end of the second flexspline.

10. A harmonic drive of claim 9, in combination with means for turning the'duplex wave generator about the common axis. a

are external and also having at the other end atthe outside an antifriction bearing race, the first fiexspline being of elliptoidal contour, a second flexspline within the first flexspline having atthe outside a set of teeth and having a second set of teeth at the inside at one end and having an antifriction bearing race at the inside at the'other end, the second fiexspline being of elliptoidal contour, the internal teeth onthe first flexspline and the external teeth on the secondfiexspline being in contact at twospaced points around the circumference with intermediate points at which they are out of contact and out of mesh, the difference in the number of teeth on the inside of the first flexspline and the outside of the second flexspline being equal to two or a multiple thereof, a first anchor of circular form surrounding the second set ofteeth on the first fiexspline and having internal teeth which are in contact with the second set of teeth on thefirst fiexspline at two spaced points around the circumference, with intermediate points at which the teeth are out of contact and out of mesh, 21 second anchor of circular. form within the second set of teeth on the second flexspline, having exter nal teeth which are in contact with the second setof teeth on the second fiexspline at two circumferentially spaced points with intermediate points at which the teeth are out of contact and out of mesh, a duplex wave generator having an elliptoidal race surrounding in spaced relation the race on theroutside of the first fiexspline and having an elliptoidalfrace within and in spaced relation to the race on the inside of the second fiexspline, antifriction bearing round'elements between the elliptoidal race surrounding the first flexspline and the race on the outside of the first fiexspline, and antifriction bearing round elements between the elliptoidal race within the second flexspline and the elliptoidal race on the inside of the second fiexspline.

14. A harmonic drive of claim 13, in which the elliptoidalraces on the wave generator are out of phase with respect to one another.

15. A harmonic drive of claim 14, in combination with means to turn the duplex wave generator around the common axis. a

16. A harmonic drive of claim 13, in combination with a circular antifriction bearing between the first and the second anchors.

References Cited in the tile of this patent UNITED STATES PATENTS 2,983,162 Musser. May 9, 1961 

